1. Field of the Invention
The present invention relates to an image display apparatus for displaying images on various plane displays on which a large number of picture elements are disposed in a matrix manner.
2. Description of Related Art
FIG. 1 is a block diagram of the principal portion of the conventional television image display apparatus disclosed in, for example, the Japanese Patent Application Laid-Open No. 56-4185, in which reference numeral 1 designates one of a larger number of picture elements disposed in a matrix on a screen (not shown), the picture element 1 being driven by a driving signal 8 from a driving signal generation unit 2. The driving signal generation unit 2 comprises a down counter 3 as a data memory and a flip-flop 4, the down counter 3 and flip-flop 4 being set by a set signal 6. The down counter 3 is loaded thereon with a television video signal 9 of data of, for example, six bits and counts clock 5. The flip-flop 4 is reset by a borrow signal 7 from the down counter 3 and gives to the picture element 1 the driving signal 8 as a signal of an output terminal Q: a Q-output.
FIG. 2 is a general view of the conventional television image display apparatus, in which the components corresponding to those in FIG. 1 are designated by like numerals. In FIG. 2, reference numeral 10 designates a screen as a display unit, in which a large number of picture elements 1 are disposed in a matrix and the driving signal generation unit 2 constructed as the above-mentioned is provided for each picture element, and 12 designates an A/D converter for digitizing an analog video signal from an input terminal 11 so as to convert it into a 6-bit data, the converted 6-bit data being outputted to a sampling unit 13. The sampling unit 13 thins data from the converted video signal and samples data only corresponding to the number of picture elements 1 on the screen 10. Each driving signal generating unit 2 is connected to a timing generation circuit 14 for generating the clock 5, set signal 6 and other predetermined timing signals and to the sampling unit 13 through transmission lines 15 comprising flat cables, the clock 5 and set signal 6 being transmitted from the timing generation circuit 14 to each driving signal generation unit 2 and the video signals 9 sampled from the sampling unit 13 being transmitted from the sampling unit 13 to the same.
Next, explanation will be given on operation of the television image display apparatus of the invention. The video signal inputted from the input terminal 11 is converted into a digital signal of 6 bits by the A/D converter 12 and subjected to sampling processing of data corresponding to the number of picture elements of the screen 10 on the basis of the predetermined timing signal obtained from the timing generation circuit 14. The sampled data is transmitted through the transmission line 15 to the driving signal generation unit 2 at each picture element 1. Simultaneously with the set signal 6 setting the flip-flop 4, the 6-bit video signal 9 is loaded on the down counter 3. Immediately, the down counter 3 counts the clock 5 and the Q-output of flip-flop 4, in other words, the driving signal 8 goes to a logical "1", so as to light the picture element 1. The down counter 3, after counting for a time corresponding to the loaded data, counts a value of (000000) so as to output a borrow signal 7, thereby resetting the flip-flop 4 and down counter 3. Accordingly, the driving signal is a logical "0" and the picture element is put out to stop the counting operation. Hence, the flip-flop 4 generates the driving signal 8 having a time length of 64 stages corresponding to the data loaded on the down counter 3 to result in that the picture element 1 is driven.
FIG. 3 shows a correspondent relation between the scanning lines and the picture elements at the television signal. FIG. 3(A) shows a mode of interlaced scanning, in which the scanning lines (1) through (6) at the odd number field represented by solid lines and those (1)' through (6)' at the even number field represented by broken lines are alternately transmitted. FIGS. 3(B) and (C) show the state whose scanning lines at the odd number and even number fields are thinned out, in which Nos. 01 through 26 and 31 through 46 show sampling points respectively, FIG. 3(D) showing the display state on the screen 10 by the sampled data.
Generally, the television signal has a sufficient amount of information, so that at the screen 10 side the data corresponding to the number of picture elements included in the screen 10 are thinned from the television signal at the sampling unit 13 to thereby be utilized. FIG. 3 shows an example in which the scanning lines (4) and (4)' are thinned corresponding to the number of picture elements vertical of the screen 10. The horizontal scanning lines are similarly thinned or the sampling cycle period is changed, so as to perform the processing corresponding to the number of horizontal picture elements on the screen 10. Since the data of each picture element 1 is updated in synchronism with the television signal at every one field (1/60 sec for NTSC system), the aforesaid operation is repeated at every picture element so as to display television images of 64 stages.
Thus, this kind of conventional display apparatus utilizes part of the amount of information included in the input television signal. Hence, the number of picture elements included in the screen 10 is restricted by the amount of information included in the television signal. For example, the number of vertical picture elements on the screen 10, when the input is in the NTSC system, is at most 240 (the number of effective scanning lines per one field at the NTSC system) picture elements.
On the other hand, there is a recent tendency of requiring high densification of display for the screen. In other words, the number of picture elements constituting the screen tends to increase, whereby the number of vertical picture elements on the screen leads to exceeding the number of scanning lines (about 240 per field in the case of NTSC system) of the television signal, for which three countermeasures therefor are considered as follows:
(1) At the display unit side, the data is interpolated after A/D conversion to thereby produce data corresponding to 240 or more scanning lines.
(2) In accordance with the timing of interlaced scanning, the data of picture element column in the odd number (or even number) lines at the display unit is rewritten to one field and the data of the even number (odd number) lines is rewritten to the next field.
(3) Like the television signal obtained by IDTV (Improved Definition Television), EDTV (Extended Definition Television), or the like, at the signal source side, scanning line interpolation is performed with respect to the television signal on the basis of timing of the interlaced scanning, thereby substantially increasing the number of scanning lines per one field.
The above-mentioned three methods each have advantages and disadvantages as follows:
The above method (1), by which all the data of the screen can be rewritten by 1/60 sec per field, is realizable of smooth mobile picture display. However, since the data is interpolated at the field portion of transmission line, an amount of information to be transmitted increases corresponding to the number of picture elements on the screen (the amount of information on the screen). Since the amount of information passable through the transmission line is limited especially when a flat cable is used as the transmission line, the size of screen capable of corresponding to the amount of information is limited.
The above method (2) can correspond to 480 vertical picture elements, two times as large as the conventional method, without increasing the data transmission speed, that is, the amount of information to be transmitted. Since the data of the display unit is rewritten at every other line on each field, the data on the screen is substantially rewritten by one frame (1/30 sec), thereby generating flickering on display.
In addition, in the method (2), there is a possibility that a further large-scale display is realizable by interpolating the data in the method (1) together. Therefore, a concrete method for the above is realized by a display unit disclosed in the Japanese Patent Application Laid-Open No. 60-158779, which is characterized in that a latch circuit is provided at the upstream side of a down counter 3 in FIG. 1. When each picture element on the scanning line at one field of interlaced scanning is driven, a display cell on the scanning line at another field is adapted to be simultaneously driven by again loading to the down counter the data latched to the preceding field, whereby the display is repeated at one field cycle period (1/60 sec) and flickering on display can be eliminated. However, since there is a time difference by one field (1/60 sec) at every line, images of high resolution is obtained with respect to the still picture, but for quick motion images, a display difference between the scanning lines corresponding to motion for 1/60 sec simultaneously appears, thereby creating the problem in that the image becomes turbulent.
Next, the method (3) has twofold 480 scanning lines per one field for both IDTV and EDTV, thereby obtaining display of high resolution, but an amount of information to be transmitted at the signal source side becomes substantially twofold, thereby creating the problem in that transmission of the information is difficult.